Add C++ solution for leetcode 224.

Author: yanglr

cpp-leetcode/leetcode224-basic-calculator_stack.cpp

@@ -0,0 +1,76 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+#include<stack>
+using namespace std;
+
+class Solution {
+public:
+    int calculate(string s) {
+        stack<int> nums; // 存储原字符串中的数
+        stack<char> ops; // 存储原字符串中的符号(含括号和+-)
+        for (int i = 0; i < s.size(); i++)
+        {
+            auto c = s[i];
+            if (c == ' ') continue; // 过滤空格
+            if (isdigit(c))
+            {
+                int n = 0;
+                int j = i;
+                while (j < s.size() && isdigit(s[j]))
+                    n = n*10 + (s[j++] - '0');
+                i = j-1;
+                nums.push(n);
+            }
+            else if (c == '(') ops.push(c);
+            else if (c == ')')
+            {
+                while (ops.top() != '(')
+                    myEval(nums, ops);
+                ops.pop();
+            }
+            else 
+            {
+                if (i == 0 || s[i - 1] == '(' || s[i - 1] == '+' || s[i - 1] == '-')  // 特殊处理符号和正号
+                    nums.push(0);                
+                while (!ops.empty() && ops.top() != '(') /* 由于此题中运算符只有+或-, 故不需要比较不同运算符的优先级了(括号前面已经处理了) */
+                    myEval(nums, ops);
+                ops.push(c);
+            }
+        }
+        while (!ops.empty()) myEval(nums, ops);
+        return nums.top();
+    }
+    void myEval(stack<int>& nums, stack<char>& ops)
+    {
+        if (ops.empty()) return;
+        int res;
+        
+        auto b = nums.top();
+        nums.pop();
+        int a = 0;
+        if (nums.size() > 0)
+        {
+            a = nums.top();
+            nums.pop();
+        }
+        auto c = ops.top();
+        ops.pop();
+
+        if (c == '+') res = a + b;
+        else if (c == '-') res = a - b;
+        nums.push(res);
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    // string s = "(1+(4+5+2)-3)+(6+8)"; //"-2+ 1";
+    string s = "1-(-2)"; //"-2+ 1";
+    auto res = sol.calculate(s);
+    cout << res << endl;
+
+    return 0;
+}